The present invention relates generally to anchors for securing sutures to bone and more specifically to threaded suture anchors adapted to be screwed into bone.
There are many surgical procedures which require attaching a suture to a bone in order that the suture may be used to hold soft tissue adjacent to the bone. Examples of such procedures include the reattachment and repair of torn tendons and ligaments in the knee, shoulder and hand. Various suture anchors have been proposed and used with varying success. U.S. Pat. No. 4,898,156 teaches a suture anchor with an elastic barb which can be pressed into a hole formed in a bone. A suture is threaded through the suture anchor and is retained in the suture anchor by a knot tied in one end of the suture. The suture anchor resists displacement due to forces on the suture because of the action of the elastic barb in digging into the side of the hole formed in the bone. U.S. Pat. No. 5,102,421 teaches a suture anchor having a series of concentric conical barbs which form a sharp point. The suture anchor is designed to be impacted into the bone. The conical barbs form a hole in the bone as they are driven into the bone and the barbs resist withdrawal of the suture anchor from the hole thus formed. A suture is attached to the suture anchor by crimping an extension of the suture anchor onto one end of the suture. Both of these prior art suture anchors provide a single strand of suture extending from the bone and fixed at one end to the bone.
Others have taught the advantages of a suture anchor secured to bone by the positive and well defined engagement of a helical screw thread with a corresponding thread formed in the bone. U.S. Pat. No. 5,632,100 teaches a suture anchor for turning into a bone. A double end of suture is attached to the suture anchor by securing a knot behind a washer pressed into a hollow end of the suture anchor. A driver engaging surface is also formed within the interior of the hollow end for receiving a driver U.S. Pat. No. 5,156,616 teaches a threaded suture anchor to which a double end of suture is attached. This suture anchor is cannulated longitudinally. The knotted suture is drawn through the cannulation and is retained in the suture anchor because the knot cannot pass through the cannulation. This suture anchor also provides an internal driver engaging surface at one end. Both of these prior art threaded suture anchors retain a suture by trapping a knot within the suture anchor and therefore the suture ends are independently fixed to the anchor. In other words, tension on either of the protruding suture ends is resisted by the knot and tension on one of the ends does not cause the other end to slide through the device.
U.S. Pat. No. Des. 331,463 depicts a threaded suture anchor having an external driver engaging portion and an extending tab for receiving a suture. This configuration for a suture anchor works well for suture anchors which are small or made of delicate materials such as bioresorbable materials. The external driver engaging portion and extending tab for the suture result in a greater cross sectional area in the body of the device than if it were designed like other suture anchors and therefore it is stronger. In addition, since the suture is attached to the anchor by being threaded through an eye in the tab, it is easier for a surgeon to attach his suture of choice to the suture anchor at the time of surgery. Also, where the suture is threaded through an eye, the suture forms a continuous length and tension on one end of the suture tends to cause the other end to slide through the suture anchor. This sliding action is advantageous in some procedures.
However, in very small anchors and especially where delicate materials are used, the extending tab may be overly weak and break under tension. Conversely, the small size of the extending tab may cause it to cut through or kink the suture. Finally, the extending tab requires that the suture anchor be driven more deeply into the bone than a suture anchor without such a tab in order to conceal the tab below the bone surface. This can make it difficult for the suture anchor to purchase cortical bone, especially where the cortical bone is thin.